Quarantine is defined as a restriction of the activities of healthy persons or animals who have been exposed to a communicable disease. The aim is to prevent transmission of the disease from potentially infected persons to healthy persons during
The word "quarantine" derives from the Italian quaranta dei (forty days), a reminder that the custom of segregating putatively infected persons, and the ships on which they were traveling, originated in the maritime empire of Venice in the fourteenth century. The length of time probably relates to the biblical story of the forty days Jesus spent in the wilderness, not to any real knowledge of the mode of transmission of infection. The rise of the practice, however, suggests that there was some understanding of the concept of contagion even if there was no empirical knowledge of infective periods and incubation times of the plagues that afflicted medieval Europe. Few infectious diseases have an incubation time or infective period greater than forty days. An exception is rabies, which may not declare itself for many months. That is why animals that may have been exposed to rabies are quarantined for many months when they arrive in countries where rabies does not exist.
Animal and plant quarantine procedures are often more important than human quarantine now that many of the most dangerous contagious diseases can be kept under observation without such draconian restrictions as formerly required. The economic importance of agriculture and animal husbandry in many countries makes it absolutely essential to exclude diseases that might wipe out valuable cattle herds or destroy a season's harvest. A very important human disease with an incubation time that can, and probably usually does, exceed forty days is HIV (human immunodeficiency virus) infection, but for reasons that have more to do with human rights than epidemiological insights there is no quarantine for persons exposed to HIV infection.
Quarantine as a way to control the spread of contagious diseases is an extreme form of isolation, which has several less severe variations. Bedside isolation, in which patients suffering from an infectious disease are barrier nursed to break the chain of transmission, is the mildest variation. More dangerous varieties of contagious disease, such as pulmonary tuberculosis with excretion of tubercle bacilli, diphtheria, and cholera, are preferably isolated in a special hospital or closed ward. Until recently, patients with such diseases as typhoid, paralytic poliomyelitis, and meningococcal meningitis were strictly isolated and every effort was made to preserve a cordon sanitaire around them. Their contacts were quarantined under public health laws in some jurisdictions, even though epidemiologically this made little or no sense as a means of preventing transmission of infection. Powerful antibiotics and better understanding have made quarantine unnecessary for these and many other diseases. Infected patients are now often treated in a general hospital rather than in one dedicated to infectious diseases. The practice of universal precautions is a modified form of quarantine in which patients with a contagious disease (such as HIV/AIDS [acquired immunodeficiency syndrome]) are barrier nursed and otherwise cared for so as to minimize the risk of HIV transmission.
Quarantine goes further than isolation because it includes the compulsory segregation of contacts of infectious cases. It therefore involves infringing upon the liberty of outwardly healthy people, and this has both legal and ethical implications. Any restriction of a person's freedom to move must be justified, and such a restriction sanctioned by public health laws and regulations in many nations. In the early twentieth century most industrial nations had lengthy lists of contagious diseases to which quarantine laws applied. By the 1960s most of these diseases could be controlled without such severe restrictions, and in 1969 the World Health Organization issued international health regulations for just four designated quarantinable diseases: cholera, plague, yellow fever, and smallpox. Smallpox was proclaimed eradicated by WHO in 1979, and the other diseases on the list (except cholera in some parts of the world and, occasionally, yellow fever in others) are now rarely encountered or respond well to medical treatment. The quarantine stations that were formerly a feature of large seaports around
Public health officials who invoke quarantine laws or regulations must justify this action ethically—on the grounds that it is in the interests of the greater good of the community. In the past, this police power of public health officials was accepted by most people as a necessary measure to control the spread of contagious disease. Community values changed in the late twentieth century, however, and there is now emotional and political resistance to restricting freedom in the interests of safeguarding the public's health. It is regarded as ethically unacceptable to quarantine promiscuous persons who are HIV-positive, even though it might be in the best interests of the general public to do so. In some places, public health officials have invoked the police power of their quarantine regulations and, sometimes with the assistance of local police forces, they have incarcerated incorrigibly promiscuous persons infected with HIV/AIDS. AIDS activists and civil rights advocates oppose this, and a debate that played out in relation to detention of polio contacts in the early twentieth century is being reprised.
JOHN M. LAST